A known general disposable body warmer comprises a breathable inner bag (enclosing bag) containing an exothermic composition, which generates heat in the presence of air; when in use, the inner bag is taken out from a non-breathable outer bag. Disposable body warmers are excellent in convenience as a heat-retaining material for the body, are provided inexpensively, and are thus recently consumed in large quantities. Disposable body warmers are subjected to disposal after use by means of landfilling or incineration. However, the inner bags used in known disposable body warmers are formed from petroleum-based plastic materials (hydrolysis-resistant materials), such as polyethylene, polypropylene, and polystyrene. Therefore, toxic gas is generated if the inner bags are disposed by incineration, and no biodegradation occurs in soil if disposed by landfilling, resulting in adverse effects on the environment.
In view of the above, attempts have recently been made to solve the above-described problems by allowing a disposable body warmer to exhibit biodegradability. Hitherto, as a technique to allow a disposable body warmer to exhibit biodegradability, there have been reports that state that a biodegradable plastic (i.e., hydrolytic biodegradable plastic), which is capable of being degraded to low molecular compound(s) through hydrolysis degradation and subsequent microbial degradation, is used in the inner bag. For example, Patent Literature 1 proposes a technique wherein a sheet material formed from a laminate consisting of a nonwoven fabric in which cellulose-based natural fibers are bonded to each other with chitosan and a film sheet mainly composed of a starch is used as the inner bag of a biodegradable disposable body warmer. Patent Literature 2 proposes a technique of using a laminate of a polylactic acid film and a natural fiber in the inner bag of a biodegradable disposable body warmer. Further, Patent Literature 3 proposes a biodegradable disposable body warmer including a biodegradable inner bag containing an exothermic composition comprising iron powder as a main component and a sodium free salt.
With respect to a disposable body warmer, the inner bag is subjected, while in use, to physical stress, such as crumpling and folding, as well as heat stress attributable to heat generation; the inner bag is thus thereby exposed to harsh environments. For this reason, the inner bag is required to exhibit physical properties (strength) that can withstand such harsh environments. However, an inner bag formed by using a hydrolytic biodegradable plastic has insufficient strength, and is gradually weakened while the disposable body warmer is in use. Therefore, known biodegradable disposable body warmers that have been reported suffer from problems such that the feeling of use worsens over time of use, and the exothermic composition is easily leaked.
As such, known disposable body warmers are not capable of exhibiting both biodegradability and desired physical properties (strength), and biodegradable disposable body warmers are thus not actually available on the market at present.
Meanwhile, an oxidative degradation agent, which allows plastic materials to depolymerize by oxidative degradation, has recently been developed (Patent Literature 4). When a plastic material comprising such a degradation agent is disposed by landfilling or other means, the plastic material is depolymerized by oxidative degradation, and then spontaneously degraded through microbial degradation. The aforementioned degradation agent is also applicable to petroleum-based plastic materials (hydrolysis-resistant materials) having high strength, and is thus attracting attention as an alternative technique for hydrolytic biodegradable plastics. However, regarding waste disposed by landfilling or other means, it is important to increase the degradation rate to thereby reduce the burden on the environment as much as possible; nevertheless, the techniques to improve the rate of degradation of a plastic material comprising such a degradation agent have not yet been sufficiently studied.